The present invention relates to a method for determining a critical angular position of a vehicle that will cause a rollover event, with one or more rotation rate sensors measuring the vehicle""s rotation rate about its longitudinal axis and/or transverse axis, and then the roll angle about the vehicle""s longitudinal axis and/or the pitch angle about the vehicle""s transverse axis is determined by obtaining the integral of the measured rotation rates so that a critical angular position can be detected therefrom via a threshold value decision unit.
A method of this kind is described in German Patent Application No. 196 09 717.1. If a vehicle undergoes a rollover, protection devices installed in the vehicle must be triggered in a timely manner; these include, for example, a roll bar, a seatbelt tensioner and various airbags. To ensure that all these protection devices are triggered in a timely manner, it is important that it be determined as early as possible whether the vehicle""s rotations about its longitudinal axis and its transverse axis will result in a rollover. It is important that as far as possible erroneous decisions regarding a rollover event be eliminated. Erroneous decisions occur if, when the integral of the rotation rate is determined, the result indicates a roll or pitch angle which does not match the vehicle""s actual angular position. Because the rotation rate sensors generally have an offset, errors may inadvertently occur when the vehicle""s angular position is calculated.
Therefore the object of the present invention is to provide a method with which as far as possible an error arising from an offset when measuring rotation rate is suppressed.
The aforementioned object is achieved in that a given rotation rate is only subjected to integration if it exceeds a lower rotation rate threshold and lies below an upper rotation rate threshold, the thresholds being predefined as a function of the offset error of the rotation rate sensor in question. The integration of the rotation rate is aborted after a predefinable reset time and restarted. This prevents a situation where, because integrals are being calculated on an ongoing basis, angles which have a value that is much greater than the actual angular position and which are then interpreted as a rollover event, which is not actually occurring, are obtained.
It is useful if the reset time is set as a function of the magnitude of the roll angle or pitch angle obtained via integration and/or as a function of the magnitude of the sensor error.